cd Desktop/backports-20131113/
make defconfig-ath9k
make
sudo make install

Reboot and let us know if it is working. You will have compiled the driver for your currently running kernel only. When Update Manager installs a newer kernel version, also known as linux-image, after you reboot, re-compile:

cd Desktop/backports-20131113/
make clean
make defconfig-ath9k
make
sudo make install
sudo modprobe ath9k